Multi-Piece Tank for Portable Restrooms

ABSTRACT

A holding tank for a portable restroom comprised of two parts, a top portion and a bottom portion, is provided. The top portion fits on the bottom portion to enclose an interior of the tank, and the top portion defines a toilet opening. The top portion preferably fits to the bottom portion with a tongue-and-groove joint. The holding tank may include additional features, such as barbs included between the top portion and the bottom portion that hold the top portion to the bottom portion. In addition, the holding tank may include a toilet bowl in the toilet opening, and the toilet bowl may be flushed by water from an internal or external fresh water vessel.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application Nos. 60/888,594 filed Feb. 7, 2007 and 60/900,500, filed Feb.9, 2007, the disclosures of which are hereby incorporated by reference.

STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

This invention relates to portable restrooms, and in particular to toilet tanks for portable restrooms.

BACKGROUND OF THE INVENTION

The increased use of portable restrooms worldwide and the substantial cost of transportation has created a need to reduce the space required for shipping the unassembled components of a portable restroom from the manufacturer to their customer, predominately a portable restroom rental company, the military or other governmental unit.

When shipping portable restrooms prior to assembly, many of the components, like the wall panels and roofs nest very closely and shipping is cost effective. Shipping the tank, traditionally molded in one piece, is not cost effective. The tank usually occupies the lower back half of a typical portable restroom, provides the toilet system, and holds waste until the unit is serviced by a pumper truck. These large hollow tanks do not nest together and typically require as much as 40% of the total space required for a shipment of the components of a load of portable restrooms.

Tanks have been traditionally molded using low cost tools adequate for low volume rotational molding, blow molding or twinsheet thermoforming processes because of variations of style and design. The three aforementioned processes used to produce tanks all produce a completely enclosed hollow tank and share one common limitation: the finished part will be comprised of a single roughly uniform thickness. The shape of the outside surface of the tank will be the shape of the inside surface. This occurs because the processes have a mold surface that creates or shapes only the outside surface. The material is forced to conform to the mold surface by centrifugal force in the case of rotational molding, air pressure in the case of blow molding, and air and vacuum pressure in the case of twinsheet thermoforming.

Injection molding uses a mold that forms both the inside and outside surfaces. It is this feature that gives the process an advantage over the other processes. Most notable is that ribs, bosses, and other intricate features can be made; additionally, section thickness can be accurately maintained. However, injection molded parts are traditionally molded with uniform wall thickness to prevent warpage and sink marks that occur as a result of material shrinkage due to cooling during and immediately following the molding process.

In certain marketplaces, a flushing mechanism for the toilet system is required. The liquid used for flushing can be either recirculated waste fluids or fresh water. When fresh water is used, an additional storage tank must be provided. Manufacturers have positioned this freshwater tank in several different places within or on a portable restroom all of which have some negative side effect. The freshwater tank occupies an already crowded space if it is inside the portable restroom.

Due to the aforementioned limitations of prior art designs, a need exists for portable restroom components that require less shipping volume and are created by more effective manufacturing processes.

SUMMARY OF THE INVENTION

The present invention relates to a holding tank for a portable restroom comprised of two parts: a top portion and a bottom portion. The top portion fits on the bottom portion to enclose an interior of the tank, and the top portion defines a toilet opening. The top portion preferably fits to the bottom portion with a tongue-and-groove joint.

In another aspect of the invention, barbs are included between the top portion and the bottom portion that hold the top portion to the bottom portion. The barbs are preferably molded integrally with the top portion or the bottom portion.

In another aspect of the invention, the holding tank may be provided with an internal fresh water holding vessel for holding water to flush a toilet bowl.

In another aspect of the invention, the holding tank may be provided with an external fresh water holding vessel for holding water to flush the toilet bowl. The external fresh water holding vessel is preferably supported on the top portion to one side of the toilet opening. The external fresh water holding vessel is also preferably taller than it is wide.

In another aspect of the invention, the toilet bowl is flushable by operation of a foot operated pump. The pump is preferably held in a housing that has a label recess.

In another aspect of the invention, a skirt may be included at a juncture between sidewalls of the bottom portion and bottom wall of the bottom portion. The skirt supports the tank on a support surface.

In another aspect of the invention, the holding tank may include an element that reduces the capacity of the tank to hold waste.

In another aspect of the invention, the top portion may include integrally molded ribs extending downwardly from a lower surface. The molded ribs angle inwardly so as to guide the top portion into engagement with the bottom portion upon assembly of the top portion to the bottom portion.

In yet another aspect of the invention, the toilet bowl may be hinged to the top portion and protrusions extend up from the top portion to engage the bowl behind a rear edge of the bowl when the bowl is pivoted to an upright position. The protrusions help hold the bowl in the upright position.

The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a toilet tank of the invention spaced up off of a portable restroom skid on which the tank would normally be supported with the toilet seat and lid removed for clarity;

FIG. 2 is a bottom perspective view of a bottom or tank portion of the toilet tank;

FIG. 3 is a view like FIG. 1 but with the tank sitting on the skid and sectioned;

FIG. 4 is a sectional perspective view of the bottom portion of the tank;

FIG. 5 is a sectional perspective view of the bottom portion of the tank;

FIG. 6 is a sectional perspective view of the of the toilet tank top and bottom assembled together;

FIG. 7 is a detail sectional perspective view of the upper rear portion of FIG. 6;

FIG. 8 is a sectional perspective view through the toilet tank top and bottom showing one embodiment of a clip to hold the top and bottom together;

FIG. 9 is a detail sectional perspective view of the clip of FIG. 9;

FIG. 10 is a perspective view of the top upside-down;

FIG. 11 is a view of a portion of the top and bottom illustrating how the ribs guide assembly;

FIG. 11 a is a detail view of the ribs of FIG. 11;

FIG. 12 is a sectional perspective view of the tops showing how the ribs of the tops assist stacking;

FIG. 13 is a perspective view of the top with a bowl assembled to it;

FIG. 14 is a view like FIG. 13 with the bowl tilted up;

FIG. 15 is a detail fragmentary view of the hinge support portions of FIG. 14;

FIG. 16 is a perspective view of a foot pump flushable toilet tank of the invention supported on a portable restroom skid;

FIG. 16 a is a detail sectional perspective view of the foot pump of FIG. 16;

FIG. 17 is a perspective view of the foot pump flushable toilet tank of FIG. 16 with an optional hinged cap;

FIG. 18 is a perspective view of a foot pump flushable toilet tank of FIG. 16 showing a tube connecting the foot pump and the tank;

FIG. 19 is a top view of the inside of the toilet tank bottom showing a filter/strainer and tubing;

FIG. 19 a is a detail view of the filter/strainer and tubing of FIG. 19;

FIG. 20 is a sectional perspective view of the toilet tank bottom showing the filter/strainer and tubing of FIG. 19;

FIG. 20 a is a detail view of the filter/strainer and tubing of FIG. 20;

FIG. 21 is a sectional view through the toilet tank showing an internal fresh water storage vessel;

FIG. 22 is a fragmentary exploded perspective view illustrating how the internal fresh water vessel is fastened to the top of the toilet tank;

FIG. 22 a is a detail perspective view of the fresh water tank of FIG. 22;

FIG. 23 is a fragmentary exploded perspective view of the top and the internal fresh water vessel of FIG. 22;

FIG. 24 is a fragmentary perspective view of the freshwater fill port cover of FIG. 17 open;

FIG. 24 a is a detail perspective view of the freshwater fill port cover of FIG. 24;

FIG. 25 is a view like FIG. 16 but with an alternative freshwater flush tank that is external to the toilet tank;

FIG. 26 is a view of a tank bottom with a reduced capacity tank installed;

FIG. 27 is a view like FIG. 26 but with the reduced capacity tank removed;

FIG. 28 is a view of a tank bottom with a bulkhead installed for reducing capacity;

FIG. 29 is a view like FIG. 26 from a different angle;

FIG. 30 is a perspective view of the freshwater tank of FIGS. 21-24;

FIG. 31 is a sectional view of the tank of FIG. 30;

FIG. 32 is a detail sectional view of FIG. 31; and

FIG. 33 is a perspective view of an alternate embodiment of an external fresh water tank shown assembled to a toilet tank.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A multi-piece portable restroom toilet tank according the present invention is to be located inside a portable restroom. The walls of the portable restroom are shown in several of the accompanying figures. However, the walls are not shown in most figures to more clearly illustrate the multi-piece portable restroom toilet tank.

Referring to FIG. 1, the multi-piece portable restroom toilet tank 10 of the present invention is a generally rectangular three-dimensional tank with a toilet system integral to a top portion 11 of the tank 10. The top portion 11 of the tank 10 includes an elevated surface 15, a recessed surface 17, and an elevated toilet surface 19. The elevated surface 15 and the recessed surface 17 are sloped downward to prevent pooling of liquids. The elevated toilet surface 19 is raised above the recessed surface 17 to provide clearance for a user's clothing and to provide a place for a toilet seat to mount. The elevated toilet surface 19 is generally arcuate and preferably extends slightly from a front edge of the top portion 11. The top portion 11 also includes an opening 18 for a vent tube (not shown) and an opening 20 for a urinal (not shown). If the unit is used without the urinal, the opening 20 can be provided with a snap cover (not shown).

The top portion 11 and the other components discussed below are light weight. This is advantageous since it simplifies loading and unloading the components from transport equipment. The top portion 11 of the tank 10 is strong enough to support a 350-pound person. To accomplish this and keep the top portion 11 lightweight, the component is made with a minimal thickness, but it is reinforced with substantially perpendicular integral ribs 52, as shown in FIG. 10, to increase its strength. The ribs 52 extend from a lower surface of the top portion 11. Where the ribs 52 terminate near the perimeter of the top portion 11 they extend downwards (toward the bottom of the tank) beyond the depth of the material at the perimeter at an acute angle towards the center of the tank 10, relative to the side of the tank 10. Therefore, the ribs 52 act as a guide to ease assembly of the top portion 11 and a bottom portion 12 of the tank 10, as shown in FIGS. 11 and l a. The ribs 52 also aid in nesting the parts when they are shipped unassembled. This aspect will be discussed in further detail below.

Referring to FIGS. 1 and 2, the tank 10 also includes the bottom portion 12 that has a bottom wall and front, rear, left, and right sidewalls extending up from the bottom wall. The bottom portion 12 is shaped such that when the unit is pumped the waste collects in a pyramid-shaped sump 13 located directly below a toilet opening 14 defined by the elevated surface 19 of the top portion 11. The bottom portion 12 includes a protruding surface 16 located below the section of the elevated toilet surface 19 that extends from the front edge of the top portion 11. The surfaces 21 adjacent the protruding surface 16 provide clearance for the user's legs and clothing. The bottom portion 12 also includes a boss 23 located near the sump 13 that will be discussed in further detail below.

Referring to FIGS. 3-5, the bottom portion 12 is also designed such that it sits on the edges of a slot of a portable restroom base and supports the weight of the user and the contents of the tank. The outer surfaces of the top portion 11 and the bottom portion 12 are smooth for easy cleaning. The bottom portion 12 of tank 10 does not have any level flat areas near the edges of the slot of the portable restroom base. This prevents solid matter from collecting on the surfaces near the edges of the slot of the portable restroom base. Therefore the support surfaces, where the tank meets the portable restroom base, are sloped towards the center of the tank 10, specifically toward the low spot 13. To fill the external gap created where the bottom portion 12 extends forward of the portable restroom base slot, an interrupted skirt or flange 60 is provided along the front and the back that extends downward from the area of the corners where the front and rear panels meet the bottom wall, as shown in FIGS. 2-5. Additionally, this skirt 60 distributes the weight of the tank 10, its contents, and a user in a proper vertical direction to the top surface of the portable restroom base. As best shown in FIG. 5, the skirt 60 has outer walls 61 that join seamlessly with the outer walls of the tank and have generally vertical reinforcing ribs 63.

Referring to FIGS. 6 and 7, the tank 10 includes components to connect the top portion 11 and the bottom portion 12. Specifically, the top portion 11 includes a two tined fork 36, or groove, and the bottom portion 12 includes a single blade 38, or tongue, that fits between the tines of the two tined fork 36. The seam 37, or tongue-in-groove joint, formed by the fork 36 and the blade 38 is located around the entire perimeter of the tank 10 where the portions 11 and 12 meet. The seam 37 enables the top portion 11 and the bottom portion 12 to be sealed or bonded together, using a suitable sealant or caulk for example, providing a leak-free joint. Other types of seams may disadvantageously leak before the tank is filled to capacity. In addition, differences of expansion and contraction of the top portion 11 and the bottom portion 12 could cause warping of sections of the tank 10 if the blade 38 of the bottom portion 12 is not trapped in between the tines of the fork 36. Lastly, the seam 37 design provides additional strength to keep the top portion 11 and the bottom portion 12 from separating if the tank is full and the restroom is impacted or tipped.

Referring to FIGS. 8-11, a fastening method is required between the top portion 11 and the bottom portion 12 because of the aforementioned hydraulic and user pressure exerted on the seam 37. A plurality of snap clips 42 located at different points on the seam 37 are incorporated in this design that include barbs 46, protruding from the blade 38 on the bottom portion 12, as shown in FIG. 9. The barbs 46 engage openings 50 in the mating surface of the top portion 11 to hold the two components together. Alternatively, the barbs 46 may be located on the top portion 11 and the openings 50 may be located on the bottom portion 12. The design of the clips 42 is such that they will engage automatically while assembling the top portion 11 to the bottom portion 12 of the tank 10. If the tank 10 needs to be disassembled, the clips 42 can be disengaged by placing a bladed tool, like a screwdriver, into the seam 37 where the clips are located, allowing the portions 11 and 12 of the tank 10 to then be pulled apart. If it is desirable to assemble the tank 10 such that it can easily be disassembled, the barbs 46 of the respective clips 42 can be removed by cutting all or some of them off.

Alternatively, the top portion 11 and the bottom portion 12 may be fastened by using standard fasteners at the seam 37, such as rivets. In addition, a combination of rivets and clips 42 may be used, such as using rivets along the front edge of the seam 37 and using clips 42 along all other edges of the seam 37.

A standard tank, commonly known as a drop tank, has no flushing apparatus. It has only a toilet seat and a cover installed on top of the elevated toilet surface 19 of the top portion 11 of the tank 10. Referring to FIGS. 13-17, a bowl 30 and a cover 31 may be provided with the tank 10. The primary reason to include the bowl 30 is to hide the contents of the tank. To adequately hide the contents of the tank, the outlet of the bowl is either closed off by a counterweighted mechanical flap or positioned to obscure the view. The opening can be aimed towards the back wall or the front wall of the tank 10. Preferably the bowl 30 includes an opening aimed towards the front wall of the tank 10. This configuration is preferred because it is most effective at obscuring the view and because of repair problems with the mechanical flap. All three of the aforementioned configurations of the bowl 30 are presently in use in the prior art.

Referring to FIGS. 14 and 15, the bowl 30 is pivotable to provide access to pump waste out of the tank 10 and maintain the system. Two protrusions 66, one at each end of a hinge pin 68 and supporting the ends of the hinge pin 68, are provided to maintain an upright position of the bowl 30 while pumping waste out of the tank 10. The protrusions 66 engage behind a flange 70 of the bowl 30 when the bowl 30 is in the upright position. The ramp like shape of the protrusions 66 allows the bowl 30 to be returned to a closed position with a simple one-handed motion.

The bowl is easily soiled because of its shape, and therefore a flushing system is preferably included. The tank 10 is configured to accommodate either a recirculating or a fresh water flushing system. The tank 10 can also be converted in the field by interchanging several parts but the pump and the bowl are provided in either system. Most current designs include components and features such as a bowl, piping and nozzle, pump, filter/strainer or freshwater storage vessel, pumping, filling, and maintenance access.

When a flushing system is used, a toilet bowl, flushing apparatus and liquid source are provided. All flushing systems include, in addition to the bowl, a pump, either hand or foot operated, a nozzle or manifold to distribute the liquid around the bowl, and tubing to transport the liquid between the source, the pump, and the bowl. If the flushing system is a recirculating system, it also includes a filter/strainer and a tube connected to the pump that is placed in the bottom of the tank to provide the source of the liquid for the system. Such recirculating systems are well known in the art. If the flushing system is a fresh water system, a source for the fresh water is provided with tubing connecting it to the pump, as described below. The pump may be either a hand pump or a foot pump. Both types of pumps may be used since each has recognized disadvantages. A foot pump may not be obvious to a user, and some users may not want to touch a hand pump, thereby leaving the toilet unflushed. The tank provided in the present invention can accommodate either type of pump without modification of the tank itself.

Referring to FIGS. 16-17, to overcome the previously mentioned shortcoming of the foot pump, the fact that it is not obvious to the user, the present invention provides a labeled housing 74 to enclose and facilitate attaching the foot pump 76 to the portable restroom. The foot pump 76 may be any type of simple pump known in the art capable of delivering liquid to the bowl 30. The housing 74 includes a bottom 78 and a top 80. The bottom 78 provides adequate space for attaching the housing 74 to the portable restroom base and positioning the foot pump 76. The top 80 overlaps the bottom 78 and has an opening for the pump diaphragm actuator. Preferably the housing 74 also has a relatively large recessed area 82 where a brightly colored label 83 that reads “FLUSH” or its translation in a different language is positioned. The recess 82 is provided to protect the edges of the label 83.

Referring to FIGS. 18-21, tubing 85 is provided to connect the various components of the flushing system. Specifically, the tubing 85 connects to the foot pump 76, passes through a hole 77 in the corner of the bottom portion 12, and connects to a filter/strainer 87 if the unit is configured for recirculated flushing. Additional tubing (not shown) is provided to connect the foot pump 76 and the bowl 30 and to provide liquid to the bowl 30. The tubing 85 is preferably fixed to the bottom of the bottom portion 12 by a bracket 79. The bracket 79 is fixed to the bottom portion 12 by a fastener (not shown) that is accommodated in the boss 23 (FIG. 2). Alternatively, standoffs (not shown) protruding upwards on the bottom of the bottom portion 12 of the tank 10 may be provided. Both the bracket 79 or the standoffs keep the filter/strainer 87 in a proper position—in the sump. The filter/strainer 87 is in this position for adequate coverage when the unit is first placed in service and there is only a small pre-charge of water and chemical in the unit. The standoffs can also be used to position and/or support a bulkhead as described below or to hold the tubing 85 routed in the interior of the tank 10.

Like prior art designs, the bowl 30 protrudes nearly half way to the bottom of the tank 10. Therefore, the waste storage capacity of the tank 10 is approximately halved. Once waste reaches the bottom opening in the bowl 30 its effectiveness in hiding the waste is negated, although there is no danger to the system if this happens. As illustrated in FIGS. 21-24, the preferred embodiment utilizes the empty space left in the upper portion of the tank 10 for an internal fresh water storage vessel 90. The internal fresh water vessel 90 is shown separate from the tank 10 in FIGS. 30-32. The internal fresh water vessel 90 includes an top section 93 and a bottom section 95. The top section 93 and the bottom section 95 may be connected by any suitable method, such as ultrasonic welding or caulking a flange section 99. The sections 93 and 95 should be designed such that they do not interfere with the top portion 11 or the bottom portion 12 of the tank 10. For example, the top section 93 includes multiple recessed areas to avoid the ribs 52 on the top portion 11. In addition, the top section 93 of the internal fresh water vessel 90 includes a hole 97 that permits access to the interior of the internal fresh water vessel 90. The surface that defines the hole 97 is slightly recessed to create a space between the internal fresh water vessel 90 and the top portion 11. This permits tubing (not shown) from the foot pump 76 to pass through the hole 97 and into the internal fresh water vessel 90. Three features are required to utilize the internal fresh water vessel 90:

1) The tank 10 must be two-piece to enable installing the internal fresh water vessel 90;

2) Components must be provided to mount the internal fresh water vessel 90 that are capable of supporting the additional weight. As shown in FIGS. 22-23, a series of bosses 91 on the underside of the top portion 11, some shown in FIG. 10, enable threaded screw-type fasteners 94 to pass through holes 92 in the flange of the custom fitted internal fresh water vessel 90 and engage the bosses 91; and

3) Access to the interior space of the internal fresh water vessel 90 must be provided. Referring to FIGS. 24 and 24 a, a port 100 may be provided in the top portion 11 with a hinged cover 102 and latching mechanism 104 for filling the internal fresh water vessel 90. The hinge feature of the cover 102 is comprised of two bent tabs 106 that are inserted through slots in the top portion 11 before placing the tank 10 in the portable restroom. Once the cover 102 is installed in the portable restroom it is not easily removed because of its close proximity to a wall. The latching mechanism of the cover 102 includes a barbed clip 108 that deflects over a ledge while closing. The ledge is formed on a tab 110 on the top portion 11 of the tank 10. The barbed clip 108 engages the ledge on the tab 110 to hold the cover 102 closed. A rib 112 around the port 100 protrudes from the top portion 11 next to and inside of the cover 102. The rib 112 is recessed behind the barbed clip 108 to require a tool to force the barbed clip 108 back into the recess to open the cover 102. The shape and position of this port 100 and cover 102 also provides a positioning and interlocking function for an external fresh water vessel, if used.

Referring to FIG. 25, an alternative position to mount a fresh water storage tank that encroaches less useable restroom space is to place it on top of the top portion 11 off to one side so it does not crowd the user. The external fresh water vessel 120 is designed taller than it is wide and its front-to-back dimension approximates that of the waste tank. The external fresh water vessel 120 is designed as such so that it holds the required amount of fresh water.

Referring to FIG. 33, which discloses an alternate embodiment of an external fresh water storage tank 140 for the tank 10, this configuration enables the placement of a handle 142 of a hand-operated flush pump 144 to be placed up away from the bowl. The handle 142 is supported by the tank 140 in a position where the user would be more familiar and comfortable with using the pump because the pump is similar to a conventional modern flush toilet valve. With the hand pump configuration, the port 100 is suitable for tubing (not shown) that passes into the storage tank. Additionally this design allows for the external fresh water tank 140 to be molded with a leg 146 that extends down to a foot pump housing 148 to provide additional support, capacity, and a location for the connections and tubing if the foot pump is substituted for the hand pump. A toilet tissue dispenser 150 could also be built into the tank 140 as illustrated. Also, with an external fresh water vessel 120 or 140, the static pressure of the water in the vessel 120 or 140 can be used to flush the bowl.

Some operators use tanks with reduced capacity as requested by their customers. As such, a secondary smaller tank 130 can preferably be inserted inside the bottom portion 12 to reduce its capacity, as shown in FIGS. 26 and 27. An alternative is to place a bulkhead divider 132 into the bottom portion 12 to reduce its capacity as illustrated in FIGS. 28 and 29.

An advantage of this design is nestability to facilitate greater unit shipping density and consequently lower shipping costs. Most tanks known to those skilled in the art are one-piece hollow units that require a relatively large shipping volume. When a tank is molded in two halves, the parts can be designed so that like parts, top portions 11 or bottom portions 12, will nest to increase shipping density. The design should incorporate integral spacers to keep the nested parts from jamming together. The bottom portions 12 of the tanks 10 of the present design nest within 2 inches of each other and have several unique features that keep the parts from jamming. Specifically, the bottom portion 12 includes a plurality of anti-jam sections 134 as shown in FIGS. 3 and 8. The anti-jam section 134 are preferably located at various positions along the perimeter of the connection between the bottom wall and the side walls of the bottom portion 12. The anti-jam sections 134 prevent a stack of bottom portions 12 from moving closer to each other and reorienting relative to one another. In addition, the interrupted skirt or flange 60 may also prevent a stack of bottom portions 12 to move relative to one another.

The ribs 52 of the top portion 11 are also integral spacers for stacking multiple components. As shown in FIG. 12, the ribs 52 extend downwards from the surface they are integral with and conform with the top surface of a like part below it in a stack. As such, a set of top panels 11 may be stacked on top of one another in the same orientation. The ribs spaced around the perimeter of the part extend the same distance and are taller than any other ribs. This permits a top panel 11 to sit horizontally when placed on a skid.

The components of the present invention are preferably made using a variation of the plastic injection molding process. This process is called structural web or gas assist injection molding. This injection molding variation is well known in the prior art. The gas assist injection molding process is as follows. The molds are first closed, and plastic resin is injected through multiple nozzles in the back of the mold. Gas, usually nitrogen, is then injected through the same nozzle. The gas passes through the hot center portion of the plastic and follows defined channels in the plastic part. After the part adequately cools, the mold opens, and the part is ejected.

Gas assist injection molding differs from standard injection molding in several ways that are advantageous to forming the components of the present invention. For example, the material is forced to the mold surfaces by gas pressure rather than injection pressure. The result of this is lower tooling cost compared to standard injection molding. This is possible because gas assist injection molds can be made from aluminum rather than steel since they do not have to withstand the relatively high pressures of standard injection molds. Additionally, the distance from the inside surface to the outside surface of the part, the wall thickness, can vary with gas assist injection molding. With this process, if there is a greater distance between the opposing surfaces in one section of the part than another, the area with the greater distance will hollow out as a result of the injected gas and the part can be made free of warp and sink marks.

As mentioned above, the present invention may include various types of flushing options. Several components for the various types of flushing options may be created in each gas assist injection molding cycle. This capability may offset the cost of details incorporated into the molded components, such as the aforementioned ribs and standoffs.

A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations to the preferred embodiment described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiment described. 

1. In a toilet holding tank for a portable restroom, the tank including a top portion and a bottom portion, the bottom portion having a bottom wall, front, rear, left, and right sidewalls extending up from the bottom wall and the top portion fitting on the bottom portion to enclose an interior of the tank, and the top portion defining a toilet opening, the improvement wherein the top portion fits to the bottom portion with a tongue-in-groove joint.
 2. A toilet holding tank as claimed in claim 1, wherein a groove of the joint is defined by the top portion and a tongue of the joint is defined by the bottom portion.
 3. A toilet holding tank as claimed in claim 1, wherein the joint is located around the entire perimeter of the tank.
 4. A toilet holding tank as claimed in claim 1, further comprising guide ribs extending downwardly from the top portion that assist fitting the top portion to the bottom portion.
 5. A toilet holding tank as claimed in claim 1, further comprising barbs between the top portion and the bottom portion that hold the top portion to the bottom portion, at least portions of the barbs being molded integrally with at least one of the top portion and the bottom portion.
 6. In a toilet holding tank for a portable restroom, the tank including a top portion and a bottom portion, the bottom portion having a bottom wall, front, rear, left, and right sidewalls extending up from the bottom wall and the top portion fitting on the bottom portion to enclose an interior of the tank, and the top portion defining a toilet opening, the improvement wherein there are snap clips between the top portion and the bottom portion that hold the top portion to the bottom portion, and at least portions of the clips being molded integrally with at least one of the top portion and the bottom portion.
 7. In a toilet holding tank for a portable restroom, the tank including a top portion and a bottom portion, the bottom portion having a bottom wall, front, rear, left, and right sidewalls extending up from the bottom wall and the top portion fitting on the bottom portion to enclose an interior of the tank, the top portion defining a toilet opening, and having a toilet bowl in the toilet opening, the improvement wherein the holding tank has an internal fresh water holding vessel for holding water to flush the toilet bowl.
 8. A toilet holding tank as claimed in claim 7, wherein the fresh water holding vessel is connected by the top portion to one side of a bowl of the toilet.
 9. A toilet holding tank as claimed in claim 7, wherein the fresh water holding vessel is fillable through a port in the top portion.
 10. A toilet holding tank as claimed in claim 9, wherein the port is closable with a cover that is hinged to the top portion and has an integrally molded barbed clip that holds the cover closed.
 11. In a toilet holding tank for a portable restroom, the tank including a top portion and a bottom portion, the bottom portion having a bottom wall, front, rear, left, and right sidewalls extending up from the bottom wall and the top portion fitting on the bottom portion to enclose an interior of the tank, the top portion defining a toilet opening, and having a toilet bowl in the toilet opening, the improvement wherein the holding tank has an external fresh water vessel for holding water to flush the toilet bowl, the external fresh water vessel being supported on the top portion to one side of the toilet opening, and the external fresh water vessel being taller than it is wide.
 12. In a toilet holding tank for a portable restroom, the tank including a top portion and a bottom portion, the bottom portion having a bottom wall, front, rear, left, and right sidewalls extending up from the bottom wall and the top portion fitting on the bottom portion to enclose an interior of the tank, the top portion defining a toilet opening, and having a toilet bowl in the toilet opening the improvement wherein the toilet bowl is flushable with operation of a foot operated pump, the pump being held in a housing and the housing having a label recess.
 13. A toilet holding tank as claimed in claim 12, wherein a label in the recess states “FLUSH”.
 14. In a toilet holding tank for a portable restroom, the tank including a top portion and a bottom portion, the bottom portion having a bottom wall, front, rear, left, and right sidewalls extending up from the bottom wall and the top portion fitting on the bottom portion to enclose an interior of the tank, and the top portion defining a toilet opening, the improvement wherein at a juncture between sidewalls of the bottom portion and the bottom wall of the bottom portion, a skirt is included that supports the tank on a support surface.
 15. A toilet holding tank as claimed in claim 14, wherein the skirt is interrupted.
 16. In a toilet holding tank for a portable restroom, the tank including a top portion and a bottom portion, the bottom portion having a bottom wall, front, rear, left, and right sidewalls extending up from the bottom wall and the top portion fitting on the bottom portion to enclose an interior of the tank, and the top portion defining a toilet opening, the improvement wherein the tank contains an element that reduces the capacity of the tank to hold waste.
 17. A toilet holding tank as claimed in claim 16, wherein the element is a tank.
 18. A toilet holding tank as claimed in claim 16, wherein the element is a bulkhead.
 19. In a toilet holding tank for a portable restroom, the tank including a top portion and a bottom portion, the bottom portion having a bottom wall, front, rear, left, and right sidewalls extending up from the bottom wall and the top portion fitting on the bottom portion to enclose an interior of the tank, and the top portion defining a toilet opening, the improvement wherein the top portion has integrally molded ribs extending downwardly from a lower surface that angle inwardly so as to guide the top portion into engagement with the bottom portion upon assembly of the top portion to the bottom portion.
 20. A toilet holding tank as claimed in claim 19, wherein the ribs support a plurality of top portions in a substantially vertical stack when the top portions are stacked one on top of another.
 21. In a toilet holding tank for a portable restroom, the tank including a top portion and a bottom portion, the bottom portion having a bottom wall, front, rear, left, and right sidewalls extending up from the bottom wall and the top portion fitting on the bottom portion to enclose an interior of the tank, and the top portion defining a toilet opening, the improvement wherein the toilet has a toilet bowl that is hinged to the top portion and protrusions extend up from the top portion to engage the bowl behind a rear edge of the bowl when the bowl is pivoted up to an upright position, so as to help hold the bowl in the upright position.
 22. A toilet holding tank as claimed in claim 21, wherein the protrusions help support a hinge pin of the bowl.
 23. A toilet holding tank as claimed in claim 11, wherein the external fresh water vessel includes a flush handle.
 24. A toilet holding tank as claimed in claim 11, wherein the external fresh water vessel has a leg extending downwardly to a housing for a foot pump flush pedal. 